You're late because you plan around the wrong number. The time on your calendar is when the meeting starts. The number that decides whether you're on time is when you have to leave: the start time, minus a realistic trip, minus the minutes around the trip.
The planning fallacy
Psychologists call our habit of underestimating how long things take the planning fallacy, a term coined by Daniel Kahneman and Amos Tversky. In a classic 1994 study, thesis students predicted on average that they'd finish in 34 days. On average it took 56.
The students had also named a worst-case date, assuming everything went wrong. About half of them missed that too.
Key idea
When we picture a plan, we picture it going right: no red lights, no lost keys, no “one quick email.”
Why travel is where it bites
Travel combines both problems. We remember a drive by its best version, the twenty minutes it took on a Sunday morning. In rush hour the same trip can take twice as long: US traffic data puts the time you need to budget to arrive on time 95% of the time at nearly double the free-flow time.
And we forget everything around the drive: finding keys, shoes, the elevator, parking, the walk from the car to the room. None of it is on the map, and all of it is on the clock.
The fix: plan backward
Stop planning forward from now. Plan backward from the start time:
- Start with the time the event begins: 3:00.
- Subtract a traffic-aware estimate for the time you'll actually be driving, not your best memory of the trip: 27 minutes.
- Subtract a buffer for getting out the door and walking in: 10 minutes.
- That's your real start time: leave by 2:23.
Keep 3:00 on the calendar, because that's when the meeting starts. Set the reminder for 2:23, because that's when you start.
The rule
For anything you have to travel to:
- Leave-by = start time − traffic-aware travel time − buffer.
- Use a live, traffic-aware estimate for when you'll actually be driving, never your best-case memory.
- Put the leave-by time on your reminder, not the start time.
